Address correspondence to: Vincenzo Suma, MD, Ultrasonic Service, Division of Obstetrics and Gynecology, Civilian Hospital, 35100 Padua, Italy. Ph: 39-49-821-3481 Fax: 39-49-821-3493.

Synonyms: Congenital gastric outlet obstruction.

Definition: Congenital malformation of the pylorus with intrinsic obliteration of its lumen.

Prevalence: Total intestinal obstructions in the upper gastrointestinal tract have an incidence of 1:10,000. Pyloric atresia represents about 1% of these anomalies, an incidence of 1:100,000.

Etiology: Unknown. Abnormality of gastric outlet development. An autosomal-recessive genetic determination is probable in familial occurrences.

Pathogenesis: Failure of recanalization after the solid stage of embryogenesis or ischemic vascular injury.

Associated anomalies: Epidermolysis bullosa, aplasia cutis congenita, esophageal atresia, omphalocele.

Differential diagnosis: Esophageal atresia and duodenal atresia.

Prognosis: Good in isolated pyloric atresia. Mortality is due to association with epidermolysis bullosa letalis.

Recurrence risk: Unknown in isolated pyloric atresia: 1:4 in subsequent siblings with epidermolysis bullosa letalis.

Management: Standard obstetrical care.

MESH Pylorus-abnormalities; Pyloric-antrum-abnormalities BDE 2617  MIM 265950 ICD9 750.5 CDC 750.580

Introduction

Pyloric atresia, an extremely rare congenital anomaly, represents less than 1% of all digestive tract atresias^1,2. We know of only two cases in which pyloric atresia was diagnosed prenatally. In one case the family was at risk for epidermolysis bullosa³, and in the other there was a familial occurrence of pyloric atresia without associated anomalies or familial recurrence.

Case #1

A 33-year-old G₂P₁₀₀₁ woman  was referred to our ultrasound unit at her 35^th week of gestation for polyhydramnios. Her past obstetrical history included a primary cesarean section for dystocia. Ultrasound examination revealed the presence of a live single fetus, with biometrical parameters (biparietal diameter, head and abdominal circumference and femur length) compatible with age, and a severe polyhydramnios. A transverse view of the fetal abdomen showed dilatation of the stomach (fig. 1).

Figure 1: Large dilatation of the stomach on a transverse view. 

The diaphragm and other abdominal organs appeared normal. A longitudinal view of the chest showed a thin, irregular tube, full of a clear fluid that seemed to be connected to the stomach. The tube ran through the chest near the left atrium of the heart to reach the base of the neck (fig. 2-3). The movements of the fetus precluded a transverse view of the chest.

Figure 2: Coronal view of the chest. The distal proximal esophagus (E) is dilated. (H = heart; S = stomach).

Figure 3: Longitudinal view of the upper chest. The distended esophagus (E) is seen. 

No other intrathoracic structural anomalies were observed, nor was there evidence of fetal hydrops. A diagnosis of suspected pyloric atresia was advanced.

At the 37^th week of gestation, a cesarean section was performed due to premature rupture of the membranes and onset of labor. A 2,700g male child was delivered. Apgar scores at 1 and 5 minutes were 7 and 10, respectively. A plain x-ray film of the abdomen, taken soon after birth, showed a typical "single bubble†in the stomach, with no air distally (fig. 4).  

Figure 4: Plain film of the abdomen. Air is seen in the stomach but not in the duodenum.

A diagnosis of pyloric atresia was made, and about two hours later the newborn underwent surgery.

The stomach was distended, and inspection of the pylorus disclosed an atresic zone. Resection of the atresia did not reveal a diaphragm but an intrinsic atretic zone. The infant was discharged after 15 days and at present is well.

Case #2

A 26-year-old P₀₀₀₀ woman, with a negative personal and family history for congenital or genetic abnormalities, was admitted to the obstetrics department for polyhydramnios and beginning labor in her 34^th week of gestation.

Ultrasound examination demonstrated the presence of a live single fetus and important polyhydramnios. Fetal biometry corresponded to the period of gestation. Morphologic evaluation of the fetus showed a markedly distended stomach (fig. 5).

Figure 5: Distended stomach. D = diaphragm, H = heart, B = bladder.

The diaphragm appeared normal. A longitudinal view of the chest showed a tube full of clear fluid connected to the stomach. This tube passed centrally throughout the chest and, in real time, alternately emptied (fig. 6) and filled (fig. 7).

Figure 6: Longitudinal view of the stomach and chest during filling.

Figure 7: Longitudinal view of the stomach and chest during emptying. 

A transverse scan of the chest, with a subcostal "four chamber†view, revealed the presence of a round cystic formation located between the aorta and the wall of the right atrium. This formation dilated and narrowed with the same pattern as the intrathoracic tube seen in the longitudinal view (fig. 8-9).

Figure 8: Four-chamber view. The emptying esophagus is seen along the left atrium. 

Figure 9: 4-chamber view. The filling esophagus is seen along the left atrium.

No other intestinal and chest anomalies were found. The diagnosis of pyloric atresia was proposed. About 2 hours later the patient delivered a live male child of 1800g. The Apgar scores at 1 and 5 minutes were 8 and 10, respectively.

A plain x-ray film of the abdomen confirmed the diagnosis (fig. 10,) and the infant underwent immediate surgery. On opening the pyloric region a diaphragm was found and opened with a 15 mm incision. The infant was discharged after 20 days with a weight of 2,120g. Currently he is well.

Discussion

There are many congenital anomalies of the gastrointestinal tract, but those affecting the stomach are extremely rare. The incidence of total intestinal obstruction of the upper gastrointestinal tract is approximately 1:10,000 neonates. Pyloric atresia represents less that 1% of these anomalies, with an incidence of 1:100,000². A recent review of the literature (1989) disclosed 125 cases of pyloric atresia, three of which were associated with esophageal atresia and 18 with epidermolysis bullosia⁵. Males and females were equally affected⁶. Low birth weight⁷ and polyhydramnios⁸ were noted in 61% of the cases.

Clinical presentation

Pyloric atresia may be suspected when non-bilious vomiting appears in the first days of life, accompanied by upper abdominal distension, with or without respiratory distress. The diagnosis is confirmed by a plain x-ray film of the abdomen showing a typical "single bubble†in the stomach with no air distally.

Pathology 

Moore⁵ recently proposed a pathophysiological classification of congenital gastric outlet obstruction due to pyloric atresia or gastric antral web (fig. 11). In most cases the defect consists of a mucosal or submucosal membrane without a muscular component. Less frequently, the pylorus is a fibrous string, or a complete segmental defect may be present.

Figure 11: The pathophysiological classification of congenital gastric outlet obstruction due to pyloric atresia or gastric web5. 1 = antral gap atresia, 2 = pyloric gap atresia, (type 1), 3 = pyloric gap atresia, (type 2), 4 = pyloric septum (solid atresia), 5 = pyloric gap atresia (type 3), 6 = pyloric membrane (type 1), 7 = pyloric membrane (type 2), 8 = antral membrane (web), 9 = antral membrane (wind sock).

Etiopathogenesis

The etiology of pyloric atresia is unknown. According to Tandler¹² this anomaly is the consequence of a failure of the tube to canalize during development. Lowe and Bernard¹³,instead, advance a mechanical cause or vascular injury. While there is no experimental evidence in support of these two theories, both are thought to explain this intestinal anomaly. In the forms associated with epidermolysis bullosa, Weber¹¹ holds that the lesion results from an intrauterine mucosal injury within junctional epidermolysis bullosa, with subsequent peptic digestion and an inflammatory scarring reaction; however, hystological examination of the pylorus carried out in one case at the 18^th week of gestation did not evidence an inflammatory reaction.

Ultrasound diagnosis

The fetal esophagus is usually situated between C₁₁ and T₉, but it escapes ultrasound imaging because it is closed during the non- functioning period, while it is dilated during swallowing. A prenatal diagnosis of congenital gastric outlet obstruction may be suspected in cases with gastric distension and polyhydramnios (61%), or in couples with risk of epidermolysis bullosa or familial occurrence of pyloric atresia. However,  specific ultrasound pictures have not yet been described.

On the basis of our observations, we believe that the ultrasound markers of this anomaly could be gastric distension and esophageal hypercontractility, which is seen with real-time scans. A longitudinal scan of the chest and abdomen (fig. 2,3,6,7) shows the markedly distended stomach and the presence of a tubular, smooth-walled, anechogenic, contractile formation. This tube originates in front of the spine to reach the upper third of the trunk, crosses the chest behind the heart and terminates in the stomach. This tubular structure is the esophagus dilated by amniotic fluid, and on real-time scan it shows an irregular peristaltic activity that corresponds to the mechanism of fetal suction and swallowing. As the swallowing and suction mechanisms are not altered, the fetus continues to swallow the amniotic fluid, which is then regurgitated due to the pyloric obstruction, thus creating an important gastroesophageal reflux. A transverse scan of the chest, with a subcostal "four chamber†view (fig. 8,9), further confirms the diagnosis because the esophagus is seen as an anechogenic, round, peristaltic mass situated between the descending aorta and the superior wall of the left atrium.

Differential diagnosis

The differential diagnosis with other upper gastrointestinal tract anomalies is based on the presence of polyhydramnios (61%), a dilated stomach and esophagus, and peristaltic esophageal waves on real-time. In esophageal atresia with or without fistula, there is no or very little fluid in the upper gastrointestinal tract. In this case, real-time ultrasonography visualizes the esophagus proximal to the site of atresia, which alternates between filling and emptying¹⁴. Esophageal atresia may also be accompanied by other malformations of the gastrointestinal tract, as well as by malformations of the heart, vertebrae, limbs and kidneys (VATER syndrome)¹⁵. Thus, the identification of any one of these abnormalities facilitates the differential diagnosis. While the classic "double bubble†is seen in the case of duodenal atresia, the findings may become less clear when esophageal atresia without fistula (4%) is present. In this case, the classic "double bubble†sign is not present.

Prognosis

The prognosis depends on the gestational age and birth weight, as well as the presence or absence of associated congenital anomalies or epidermolysis bullosa. In cases without other malformations, the prognosis is usually good. Only a few reports describe rupture of the stomach¹⁷ and aspiration pneumonia as the result of a delay in the diagnosis. Prematurity and low birth weight with respiratory complications (hyaline membrane disease) are thought to be related to polyhydramnios, causing preterm labor. The prognosis is unfavorable when both pyloric atresia and epidermolysis bullosa are present. The prenatal diagnosis of isolated pyloric atresia should greatly improve the prognosis, compared to cases diagnosed after birth.

Recurrence risk

Familial occurrence has been reported, and an autosomal recessive transmission has been advanced^9-10.

Obstetrical management

Since prenatal diagnosis of pyloric atresia has not been previously reported and considering our two cases, we believe that obstetrical management should not change. Polyhydramnios may contribute to the onset of premature labor; tocolytic agents are indicated in these patients and amniotic fluid drainage may also be considered. The antenatal administration of steroids in cases of lung immaturity is indicated. Genetic counseling must be offered to couples with pyloric atresia-epidermolysis bullosa syndrome, since the risk of an affected child is 25%.

Epidermolysis bullosa can be diagnosed prenatally at the 18^th week of pregnancy with a skin biopsy performed via fetoscopy. Given the high neonatal mortality rate of this syndrome, couples should be given the option to terminate the pregnancy in due time. Delivery in a specialized center is recommended, as these infants will require immediate surgical care.

References

1. Korber JS, Gasson MJ: Pyloric atresia associated with  epidermolysis bullosa. J Pediatr 90:600-1,1977.

2. Thompson NW, Parker W, Schwarts S, et al.: Congenital pyloric atresia. Arch Surg 97:792-6,1968.

3. Nazzaro V, Nicolini U, De Luca L, et al: Prenatal diagnosis of junctional epidermolysis bullosa associated with pyloric atresia. J Med Genet 27:244-8,1990.

4. Peled Y, Hod M, Friedman S, et al.: Prenatal diagnosis of familial congenital pyloric atresia. Prena Diagn 12:151-4,1992.

5. Moore CM: Congenital gastric outlet obstruction. J Pediatr Surg 24:1241-6,1989.

6. Kume K, Ikeda K, Hayashida Y, et al.: Congenital pyloric atresia: a report of three cases and review of the literature. J Pediatr Suirg 16:259-68,1980.

7. Bronsther B, Nadeau MR, Abrams MW: Congenital pyloric atresia. A report of three cases and a review of the literature. Surgery 69:130-6,1971.

8. Duchersne JC, Benoussan AL: Pyloric atresia. J Pediatr Surg 10:149-50,1975.

9. Olsen L, Gratte G: Congenital pyloric atresia: report of a familial occurrence. J Pediatr Surg 11:181-4,1976.

10. Bar-Maor JA, Nissan S, Nevo S: Pyloric atresia. A hereditary congenital anomaly with autosomal recessive transmission. J Med Genet 9:70-2,1971.

11. Weber M: Hemidesmosome deficiency of gastro-intestinal mucosa, demonstrated in a child with Herlitz syndrome and pyloric atresia. Acta Derm Venereol (Stockholm) 67:360-2,1987.

12. Tandler J: Zur Entwicklungsegeschichte des menschlichen Duodenum im fruhen embryonens stadium. Gerenbaur. Morph Gahng 29:187-216,1900.

13. Lowe JH, Bernard CN: Congenital intestinal atresia: observations on its origin. Lancet 269:1065-7,1953.

14. Eyeremendy E, Pfister M: Antenatal real-time diagnosis of aesophageal atresia. JCU 11:395-7,1983.

15. Quanl, Smith DW: The Vater association: vertebral defects, anal atresia, tracheoesophageal fistula with esophageal atresia, radial dysplasia. Birth Defects 8:75,1972.

16. Boychuk, Lyon EA, Goodhand TK: Duodenal atresia diagnosed by ultrasound. Radiology 127:500,1978.

17. Sloop RD, Montagne ACW: Gastric outlet obstruction due to congenital pyloric mucosal membrane. Am Surg 165:598-604,1967.